** Next:** Bohr model of the
**Up:** Early models of the
** Previous:** Early models of the

It turns out however that there are serious problems with this
simple planetary model of the atom.
These relate to the
fact that the electron, in orbiting the nucleus, undergoes an
acceleration (recall that an acceleration arises from a change in velocity,
which can be a change in speed and/or a change in the direction of
motion). Maxwell's theory of electromagnetism then predicts that any charge
which is accelerated will emit electromagnetic radiation; for example,
X-ray machines produce X-rays by accelerating electrons through fairly
high potential differences. Thus, in this model we would expect the
electron to be continuously emitting radiation, and as it does it would
lose energy, and eventually collapse into the nucleus.
At first these were thought to be good features of the model, as
it was known that atoms do emit light when heated, and also that many
atoms, particularly the heavier ones, do have a finite lifetime.
However, quantitatively the predictions
are completely wrong. The light that comes from atoms of a given
element occurs only with a certain set of discrete frequencies, whereas the
light emitted in this model contains a wide range of frequencies.
Furthermore, the time of collapse of any atom in this model turns out
to be of the order of 10^{-9} s, which is much too short compared to
the lifetimes of, in particular, the lighter atoms, which are relatively
stable.

** Next:** Bohr model of the
**Up:** Early models of the
** Previous:** Early models of the
*modtech@theory.uwinnipeg.ca *

1999-09-29